Catalytic hydrogenation of sulfurbearing hydrocarbon oils



CATALYTIC HYDROGENATION F SULFUR- BEARING HY DROCARBON OILS Jacob Koomeand Gerardus J. F. Stijntjes, Amsterdam,

Netherlands, assignors to Shell Oil Company, a corporation of DelawareN0 Drawing. Filed Feb. 11, 1958, Ser. No. 714,497

Claims. (Cl. 208-416) This invention relates to the catalytichydrogenation of sulfur-bearing hydrocarbon oils boiling at least 90% byvolume above 300 C. or above 450 C.

Various high boiling hydrocarbon oils have been hydrogenated underconditions of temperature, pressure and contact time, depending upon theparticular catalyst and particular oil feed, to efiect a substantialconversion of the oil to lower boiling products. When carried out withthis result such operation is referred to as destructive hydrogenationor hydrocracking. While hydrocracking is a desirable process in somecases, there are cases where hydrocracking is undesired and is avoided,e.g. in the hydrogenation of lubricating oil, transformer oil, etc.

Hydrogenation under conditions where not more than about of the feed oilis converted to lower boiling products is often called non-destructivehydrogenation. There is usually at least a small amount of lower boilingmaterial unavoidably produced, e.g. 2-5 due to a lowering of the boilingpoint upon extracting a sulfur atom from the sulfur compounds which arenormally present in the feed but hydrocracking is suppressed. Theprocess of the present invention is a process of this latter ornondestructive type.

The non-destructive hydrogenation of hydrocarbon oils may be efiected inseveral ways. In one type of operation, for instance, sulfur-bearingoils are hydrogenated with a catalyst containing a metal or metal oxidewhich is capable of taking up sulfur from the oil and reactingtherewith. In this type of process, which may be called regenerative,the process is stopped as soon as the metal has been substantiallyconverted to the sulfide (which is manifested by the appearance ofhydrogen sulfide in the reactor efliuent), the catalyst is re-oxidizedor roasted to convert the metal sulfide back to the active oxide ormetallic form and a new process period is then started. The processperiods between successive oxidations or roastings of the catalyst arenormally quite short. Since it is necessary to free the catalyst of oilpreceding each oxidau'on or roasting step, it is only practical tooperate this type of process when treating low boiling easilyvolatilized feeds or to ensure that the feed oil, if heavy, iscompletely vaporized by the use of a large amount of gas.

The more preferred type of hydrogenation process is one in which the oiland hydrogen gas are passed substantially continuously in contact with afixed bed of a suitable metal sulfide catalyst. The process of thepresent invention is of this type, referred to as non-regenerative. Thusany regeneration that may be required is only required after arelatively long period of continuous use usually measured in Weeks ormonths.

When hydrogenating sulfur-bearing oils by this latter ornon-regenerative kind of process it is found that as the molecularweight (and hence boiling point) of the feed oil is increased the rateof hydrogenation declines. Thus, when the feed oil is one which boils atleast 90% by volume above 300 C., and especially one which boils atleast 90% by volume above 450 0,, it is generally oil.

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not possible to elfect the desired hydrogenation at space rates that areeconomically attractive. In Drennan pat ent, US. 2,365,751, this problemis touched upon (note page 2, column 2, lines 7-15) and it is proposedeither to lengthen the reactor or to employ two or more reactorsconnected in series. This solution amounts to a reduction in the spacevelocity.

The extent of this difficulty may be seen from the following comparativetests. A West Texas crude petroleum was fractionated to separate fourfractions of increasing boiling point as follows:

TABLE 1 Fraction 1 2 3 4 Boiling range, O

TABLE II Fraction 1 2 3 4 Time in Hours 1 300 s.c.fJb 1. 5 400 s.e.f./b4

1 Taken from a plot of H2 uptake vs. time. 2 During this time fractionNo. 1 took up ca 650 s.c.lJb.

The drastic reduction in hydrogenation rate with increasing molecularweight is clearly evident.

When the above fractions were blended in their original ratio and themixture was hydrogenated under the same conditions it was found that therate of hydrogen uptake was somewhat slower than the rate calculatedfrom the rates of the individual fractions. Thus, whereas one would haveexpected 400 s.c.f./ b. of hydrogen to be taken up by the blend in about6 hours, a time of about 8 /2 hours was actually required. This wouldindicate that the best results would be obtained by hydrogenating theindividual fractions separately.

In the process according to the invention the hydrogenation of heavyoils is effected in a particular Way, referred to herein as the trickletechnique. This technique is substantially as described in Hoog patent,US. 2,608,- 521. It is found using the trickle technique under theconditions later set forth that the hydrogenation of heavy oils ismaterially improved if the heavy oil is hydrogenated in the presence ofa suitable lower boiling auxiliary A possible explanation for thisunexpected result may be seen from the results of the following tests.

A hydrocarbon oil containing both light and heavy components (boilingrange ca 221 C. to above 477 C.) was fractionated into five narrowfractions and these fractions carefully analyzed in detail. A portion ofthis oil was hydrogenated using the trickle technique in a 2" diameterreactor under the following conditions.

TABLE III Catalyst. 6-14 mesh The product from this hydrogenation wasthen fractionated as before and the fractions carefully analyzed. Fromcomparison of the analyses of the corresponding unhydrogenated andhydrogenated fractions it was possible to calculate the disposition ofthe consumed hydrogen. Such calculation indicated that the lightest 20%wof the oil had taken up only about 90 s.c.f./b. whereas the heaviest 20%of the oil had taken up about 640 s.c.f./b. This unexpected result wasconfirmed in another case with a different oil. This oil washydrogenated using the trickle technique to a total hydrogen uptake ofabout 220 s.c.f./b. The higher and lower boiling halves of this oil werecarefully analyzed and compared to the corresponding parts of theuntreated oil. It was found that the lower boiling half had consumedapproximately 70 s.c.f./b. whereas the higher boiling half had consumedapproximately 346 s.c.f./b.

As will be demonstrated by examples, the process of the invention allowsheavy oils to be hydrogenated more effectively.

The process of the invention is effective for the hydrogenation ofvarious hydrocarbon oils which boil essentially above 300 C., i.e. atleast 90% by volume boils above 300 C. It is particularly useful for thehydrogenation of hydrocarbon oils boiling essentially above 450 C., i.e.at least 90% by volume boils above 450 C. Thus it is possible toeifectively hydrogenate the residues remaining after the vacuum or steamdistillation of crude oil. These latter oils, if residues, arepreferably first subjected to a deasphalting treatment, e.g. withpropane and/or butane in the known manner. Another type of materialwhich may be hydrogenated by the process of this invention is ahydrocarbon distillate over 90% of which boils above 300 C. and no morethan 20% of which boils above 500 C., e.g. lubricating oil distillates.In the case of these higher boiling oils it is customary to effect theactual distillation under vacuum or with steam to prevent excessivecracking and then to calculate the corresponding boiling points atatmospheric pressure. These higher boiling oils from natural sourcesnormally contain from appreciable to considerable amounts of sulfurcompounds and other impurities.

These oils are hydrogenated in the presence of an auxiliary oil having aboiling range entirely or substantially entirely below that of the heavyoil to be treated. The boiling range of the auxiliary oil may adjointhat of the heavy oil without a gap. A slight overlap of the boilingranges is also possible, e.g. 90% by volume or more boiling below theinitial boiling point of the heavy oil. A complete separation of thehydrogenated heavy oil fraction from the auxiliary oil in the treatedmixture by fractional distillation is of course impossible in thesecases. On the other hand, the separation of the two oils by distillationis greatly facilitated by the use of an auxiliary oil having a finalboiling point several degrees, e.g. at least 25 0, below the initialboiling point of the heavy oil thereby form a distinct gap. In any casethe auxiliary oil isobtained as a separate fraction and then added tothe oil fraction to be hydrogenated. Examples of auxiliary oils having aboiling range entirely or substantially below that of the heavyhydrocarbon oil to be hydrogenated are kerosene, gas oil, and flasheddistillate. The auxiliary oil may be produced by the distillation ofcrude petroleum oils or from similar boiling range materials obtainedfrom oils subjected to thermal or catalytic treatment. The cycle stocksobtained in the catalytic cracking of heavy oil fractions are quitesuitable when in the desired boiling range.

The auxiliary oil is preferably a substantially saturated oil, i.e. onewhich contains little or no olefins or diolefins, and is-preferably arelatively heavy oil, although lighter than the oil to be hydrogenated.The reason for this is that oils boiling below about 200 C. atatmospheric pressure vaporize excessively in the hydrogenation operationthereby increasing the extent of vaporization of the heavy oil anddiluting the hydrogen.

While the lower boiling auxiliary oil is essential its amount is notvery critical. Thus, for an example, a straight run heavy Kuwait gas oilwas hydrogenated using a kerosene (IBP=250 C.) as the auxiliary oil inamounts corresponding to 10, 20 and 30% in the blends. A substantialimprovement Was obtained when the auxiliary oil constituted only 10% ofthe mixture (i.e. 1:9 ratio) but there was little further improvement inthe blends containing 20 and 30% of the auxiliary oil. It is withininvention to use still higher concentrations of the auxiliary oil up toand including at least 1.25 parts by weight per part of the heavy oil.

The present process is carried out using a catalyst comprising at leastone element of group VIII, preferably Ni and/or Co, and one element ofgroup VI of the periodic table of the elements, preferably Mo and/or W,and, if desired, a support, preferably alumina. A particularly suitablecatalyst is one containing 5 to 15% of cobalt in an atomic ratio between1:10 and 9:10 supported on an activated alumina support which mayinclude a small amount (110%) of silica and a trace (0.1-1%) offluorine.

The metals may be present initially in their metallic form or in theform compounds with oxygen or sulfur. During use they are howeverpresent in the form of sulfides. Thus the catalyst may be presulfided orit may become sulfided during the process itself. A preferredpretreatment is to pass hydrogen and a liquid oil containing a largeamount of sulfur, i.e. at least 1% S, over the catalyst starting at alow temperature below about C. and then gradually increase thetemperature to the desired operating temperature over a period of atleast several hours.

As mentioned above, the hydrogenation is effected according to theinvention in a particular way called the trickle technique. The mixtureof the heavy oil and the auxiliary oil is passed continuously in theliquid phase with gas consisting predominently of hydrogen downwardlythrough a foraminous bed of the catalyst. The liquid flows down in theform of a thin film on the surface of the catalyst particles. Thus theoil rate should not be sufficiently high to flood the bed.

It is preferred that the oil to be hydrogenated and the auxiliary oil bewell mixed and contacted with the gas before contacting the catalystsince this ensures that the oil contacting the catalyst containsdissolved hydrogen. Y

The amount of gas consisting mainly of hydrogen supplied with the oilshould be such. that after cooling the reaction product and removinghydrogen sulfide from the uncondensed gas thequantity of the latter gasis at least 50 liters (measured H 8 free at 0 C. and 1 atm.) perkilogram of the heavy oil plus auxiliary oil fed to the reaction zone.This is equivalent to about 240 s.c.f./b. On the other hand, the amountof exit gas is preferably not too large since large amounts of gasinsuflicient to effect complete vaporization of all of ,the oil tends tocause vaporization of a large part of the feed .oil leaving a thicktarry material, which does not trickle properly. The quantity ofuncondensed gas freed ofhydrogen sulfide leaving the reaction spacepreferably lies between 50 and 600 liters per kilogram of the oilmixture supplied. This off gas is in part recycled to the reactorpreferably after treating it to remove hydrogen sulfide. Sufficientfresh hydrogen is supplied to maintain the hydrogen content in the gasfed to the reactor above about 50%. The hydrogenation is effected attemperatures between 325 and 500 C., more preferably between 325 and 400C. The operating pressure is in the range of from 10 to 100 atm. and ispreferably in the range of from 25 to75 atm. These conditions arecorrelated such that the oil remains largely in the liquid phase.

After the described hydrogenation treatment the auxiliary oil may beseparated from the hydrogenated heavy oil by distillation with orwithout the use of vacuum or steam. If, as in the preferred case thereis a gap, e.g. 25 C. or more, between the boiling ranges of the twooils, this separation may be made quite cleanly. Otherwise there will besome smearing. Such smearing is generally undesired but is notobjectionable in some cases, e.g. in the hydrogenation of catalyticcracking feed stock.

When hydrogenating heavy oils according to the process of this inventionit is found that the oils are much more deeply hydrogenated at a giventhruput rate than if the heavy oil were treated alone using the trickletechnique; For example, if a heavy oil is hydrogenated alone using aspace velocity of 0.5 kg/L/hr. the extent of hydrogenation as indicatedby the percent desulfurization may be in a typical case about 55 to 60%Whereas if a suitable auxiliary oil is added to the heavy oil and themixture is passed through the reactor at a space velocity of lkg./l./hr. so that the heavy oil is being treated at the same rate as'inthe case where it was not mixed with the auxiliary oil, the extent ofhydrogenation as indicated by the percent desulfurization issubstantially greater, e.g. 70-75%. At the same time a major proportionof the sulfur in the auxiliary oil is removed.

Example I From a Venezuelan crude petroleum a number of distillatefractions and a residue were separated in a conventional manner bydistillation at atmospheric pressure and subsequent distillation undervacuum. The residue remaining was deasphalted with butane. The resultingdeasphalted heavy oil boiled above 450 C., (90% by volume above 492 C.)and had a sulfur content of 2.73% by weight. This heavy hydrocarbon oilfraction was hydrogenated using the trickle technique and within theconditions specified above. The catalyst was a cobalt-molybdenum-aluminacatalyst containing about 3.1% Co and 7.1% M Three carefully controlledtest runs (C, D and E) were carried out under the conditions and withthe results shown in Table IV. Test runs C and D were performed on theheavy oil as such, the conditions differing only as regards the spacevelocity. Test run E was according to the invention. To the heavydeasphalted residue there was added a flashed distillate (90% by volumedistilled up to 490 C.) in a weight ratio of about 1.25:1. Forcomparison purposes two test runs A and B were carried out with theflashed distillate in the absence of the heavy oil.

All runs carefully controlled to these values, slight variations wereunavoidable.

The hydrogenated mixture of flashed distillate and deasphalted residueobtained in experiment E was separated 6. by distillation into twofractions in the same ratio by weight as in the starting mixture. Theflashed distillate was found to have been 93% desulfurizedbyhydrogenation, i.e. to the same degree as that attained in thehydrogenation of the flashed distillate separately at the same spacevelocity (1.0). However, the deasphalted residual oil was found to havebeen 74% desulfurized instead of 49% which occurred at the same spacevelocity when there was no previous dilution of this oil with theauxiliary oil. This shows a much greater extent of hydrogenation.Comparison with the results in columns B, D, and E shows that in thecase of the combined Example I] The heavy oil fraction treated was aparaffinic lubrieating oil obtained from a Venezuelan crude oil. Thisfraction had a sulfur content of about 2.11% by weight, an initialboiling point of about 350 C. and 80% by volume distilled over atemperature of about 484 C. (The distillation was carried out under apressure of 10 mm. Hg and the boiling temperatures measured were thenconverted to the corresponding value at atmospheric pressure.) Thisheavy hydrocarbon fraction was then hydrogenated using the trickletechnique and Within the conditions specified above. The catalyst wasthe same cobalt-molybdenum-alumina catalyst as described in Example I..Three I'llllS (F,.G and H) were carried out under the conditions andwith the results shown in Table V. Experiments F and G were made withthe heavy fraction as such, the conditions difiering only as regards thespace velocity. Run H was according to the present invention. To theheavy fraction there was added a kerosene boiling from 187 to 261 C.(A.S.T.M.) in a ratio of 1:1 by weight. The kerosene contained 0.34% byweight sulfur. For comparison purposes two runs (I and J) were carriedout with kerosene in the absence of the heavy oil; the results are alsoshown in Table II.

The mixture of lubricating oil and kerosene obtained in experiment H wasseparated by distillation into a kerosene fraction and a lubricating oilfraction.

TABLE V Run F G H I J Lubri- Feed Lubricating eating Kerosene Oil oilKerosene Sulfur content, percent by weight 2.11 Pressure, kg./sq. cm. 5050 Temperature, 0... 385 Quantity of HZS-irce gas leaving the reactionspace in liters (standard conditions) per kg. of oil 250 250 250 Spacevelocity, kg./l./hr. 1.0 0.5 1.0 1.0 0.5 S in total quantity of reac 11product, percent 0.86 0.58 0.14 0.001 0.001 S in lubricating oil,percent..- 0.86 0.58 0.311 S in kerosene, percent 0.007 0.001 0. 001Total desulfurization, percent. 59.3 72. 5 88.5 I 99 99 Desulfurizationof the lubricating oil, percent 59.3 72.5 85.3 Desulfurization of thekerosene,-

percent 97 99 99. 6

The kerosene was found to have been 97% desul furized, i.e.tdsubstantially the same degree as that att ained in the hydrogenationof the kerosene separately at the same space velocity (1.0). However,the lubricating oil was found to have been 85.3% desulfurized instead of59.3% which occur-red at the same space velocity (1.0) when the oil wasnot previously diluted with kerosene.

The above data clearly show that when operating according to theinvention at a space velocity of 1.0 kg./l/hr. the hydrogenation of thelubricating oil is considerably improved as indicated by the greaterpercent desulfurization (85.3 instead of 72.5). At the same time thedesulfurization of the auxiliary oil (kerosene) is only slightly lowerthan in the case of the separate treatment of this material at a spacevelocity of 0.5 kg./1/hr. (97% instead of 99.5%).

We hereby claim as our invention:

1. An improved process for the continuous nondestructive hydrogenationof sulfur-bearing lubricating oil boiling at least 90% by volume above300 C. but not more than about 2 by volume above 500 0, withoutconversion of more than about 10% by volume of said lubricating oil tolower boiling products, which comprises the steps of (1) admixing thelubricating oil to be hydrogenated with an auxiliary oil at least 90% byvolume of which boils below the initial boiling point of the lubricatingoil, the amount of the auxiliary oil being from about 0.10 to about 1.25parts by weight per part of the lubricating oil, (2) mixing theadmixture of lubricating oil and auxiliary oil with ahydrogen-containing gas, (3) passing the mixture of lubricating oil,auxiliary oil and hydrogen-containing gas downwardly through aforaminous bed of a hydrogenation catalyst in a reaction zone, thecatalyst comprising as active hydrogenation promoters sulfides of ametal of group VI and metal of group VIII, at a rate insufficient toflood the catalyst so that the oil flows as a film over the catalystparticles, while maintaining the temperature in the reaction zone aboveabout 325 C. but below about 400 C. and the pressure above about 10 atm.but below about 100 atm., said temperature and pressure being correlatedto maintain the oil largely in the liquid phase, and the amount ofhydrogen-containing gas being such that the eflluent gas from thereaction zone contains between 50 and 600 liters (measured as H 8 freegas at 0 C. and 1 atm.) per kilogram of lubricating oil charged.

2. An improved process for the continuous nondestructive hydrogenationof sulfur-bearing lubricating oil boiling at least 90% by volume above300 C. but not more than about 20% by volume above 500 C., withoutconversion of more than about 10% by volume of said lubricating oil tolower boiling products, which comprises the steps of (l) admixing thelubricating oil to be hydrogenated with a kerosene, auxiliary oilboiling essentially above 200 C. and having a final boiling pointsubstantially below the initial boiling point of the lubricating oil,the amount of the auxiliary oil being from about 0.10 to about 1.25parts by weight per part of the lubricating oil, (2) mixing the mixtureof lubricating oil and auxiliary oil with a hydrogen-containing gas, (3)passing the mixture of lubricating oil, auxiliary oil andhydrogen-containing gas downwardly through a foraminous bed of ahydrogenation catalyst in a reaction zone, the catalyst comprising asactive hydrogenation promoters sulfides of a metal of group VI and metalof group VIII, at a rate insufficient to flood the catalyst so that theoil flows as a film over the catalyst particles, while maintaining thetemperature in the reaction zone above about 325 C. but below about 400C. and the pressure above about 10 atm. but below about 100 atm., saidtemperature and pressure being correlated to maintain the oil largely inthe liquid phase, and the amount of hydrogen-containing gas being suchthat the eflluent gas from the reaction zone contains between 50 and 600liters (measured as H S free gas at 0 C. and 1 atm.) per kilogram oflubricating oil charged.

3. Process according to claim 1 in which the final boiling point of theauxiliary oil is at least 25 C. below the initial boiling point of thelubricating oil.

4. An improved process for the continuous nonde-. structivehydrogenation of sulfur-bearing lubricating oil boiling at least byvolume above 300 C. but not more than about 20% by volume above 500 C.,without conversion of more than about 10% by volume of said lubricatingoil to lower boiling products, which comprises the steps of (l) admixingthe lubricating oil to.

be hydrogenated with an auxiliary oil at least 90% by volume of whichboils below the initial boiling point of the lubricating oil, the amountof the auxiliary oil being from about 0.10 to about 1.25 parts by weightper part of the lubricating oil, (2) mixing the admixture of lubricatingoil and auxiliary oil with a hydrogen-containing gas, (3) passing themixture of lubricating oil, auxiliary oil and hydrogen-containing gasdownwardly through a forarninous bed of a hydrogenation catalyst in areaction zone, the catalyst comprising as active hydrogenation promoterssulfides of a metal of group VI and metal of group VIII, at a rateinsufficient to flood the catalyst so that the oil flows as a film overthe catalyst particles, while maintaining the temperature in thereaction zone above about 325 C. but below about 400 C. and the pressureabove about 10 atm. but below about atm., said temperature and pressurebeing" correlated to maintain the oil largely in the liquid phase, andthe amount of hydrogen-containin gas being such that the efiluent gasfrom the reaction zone contains between 50 and 600 liters (measured as HS free gas at 0 C. and 1 atm.) per kilogram of lubricating oil charged,and (4) separating the reacted mixture by distillation into twofractions having boiling ranges substantially similar to those of theoriginal lubricating and auxiliary oils.

5. An improved process for the continuous nondestructive hydrogenationof sulfur-bearing lubricating oil boiling at least 90% by volume above300 C. but not more than about 20% by volume above 500 C., withoutconversion of more than about 10% by volume of said lubricating oil tolower boiling products, which comprises the steps of (1) admixing thelubricating oil to be hydrogenated with an auxiliary oil at least 90% byvolume of which boils below the initial boiling point of the lubricatingoil, the amount of the auxiliary oil being from about 0.10 to about 1.25parts by weight per part of the lubricating oil, (2) mixing theadmixture of lubricating oil and auxiliary oil with ahydrogen-containing gas, (33) passing the mixture of lubricating oil,auxiliary oil and hydrogen-containing gas downwardly through aforaminous bed of a hydrogenation catalyst in a reaction zone, thecatalyst comprising as active hydrogenation promoters sulfides of ametal of group VI and metal of group VIII, at a rate insufiicient toflood the catalyst so that the oil flows as a film over the catalystparticles, while maintaining the temperature in the reaction zone aboveabout 325 C. but below about 400 C. and the pressure above about 10 atm.but below T about 100 atm., said temperature and pressure being cor-References Cited in the file of this patent UNITED STATES PATENTS

1. AN IMPROVED PROCESS FOR THE CONTINUOUS NONDESTRUCTIVE HYDROGENATIONOF SULFUR-BEARING LUBRICATING OIL BOILING AT LEAST 90% BY VOLUME ABOVE300* C. BUT NOT MORE THAN ABOUT 20% BY VOLUME ABOUVE 500* C., WITHOUTCONVERSION OF MORE THAN ABOUT 10% BY VOLUME OF SAID LUBRICATING OIL TOLOWER BOILING PRODUCTS, WHICH COMPRISES THE STEPS OF (1) ADMIXING THELUBRICATING OIL TO BE HYDROGENATED WITH AN AUXILIARY OIL AT LEAST 90% BYVOLUME OF WHICH BOILS BELOW THE INITIAL BOILING POINT OF THE LUBRICATINGOIL, THE AMOUNT OF THE AUCILIARY OIL BEING FROM ABOUT 0.10 TO ABOUT 1.25PARTS BY WEIGHT PER PART OF THE LUBRICATING OIL, (2) MIXING THEADMIXTURE OF LUBRICATING OIL AND AUXILIARY OIL WITH AHYDROGEN-CONTAINING GAS, (3) PASSING THE MIXTURE OF LUBRICATING OIL,AUXILIARY OIL AND HYDROGEN-CONTAINING GAS DOWNWARDKY THROUGH AFORAMINOUS BED OF A HYDROGENATION CATALYST IN A REACTION ZONE, THECATALYST COMPRISING AS ACTIVE HYDROGENATION PROMOTERS SULFIDES OF AMETAL OF GROUP VI AND METAL OF GROUP VIII, AT A RATE INSUFFICIENT TOFLOOD THE CATALYST SO THAT THE OIL FLOWS AS A FILM OVER THE CATALYSTPARTICLES, WHILE MAINTAINING THE TEMPERATURE IN THE REACTION ZONE ABOVEABOUT 325* C. BUT BELOW ABOUT 400* C. AND THE PRESSURE ABOVE ABOUT 10ATM. BUT BELOW ABOUT 100 ATM., SAID TEMPERATURE AND PRESSURE BEINGCORRELATED TO MAINTAIN THE OIL LARGELY IN THE LIQUID PHASE, AND THEAMOUNT OF HYDROGEN-CONTAINING GAS BEING SUCH THAT THE EFFLUENT GAS FROMTHE REACTION ZONE CONTAINS BETWEEN 50 AND 600 LITERS (MEASURED AS H2SFREE GAS AT O* C. AND 1 ATM.) PER KILOGRAM OF LUBRICATING OIL CHARGED.